Hi team, 

I have a number of Samba servers that perform "net ads testjoin -P" on a schedule. 

This net process sometimes gets stuck in endless loop, using 100% of the CPU. This only started to happen with upgrade to Samba 3.6.13 or later, but I cannot tell when exactly. It's happening now with 3.6.22. 

Here is a stack trace of a running process from gdb: 

(gdb) bt
#0  0x00007fff8e1ff771 in gettimeofday ()
#1  0x00007f4589cf532b in ?? () from /usr/lib/x86_64-linux-gnu/libkrb5.so.3
#2  0x00007f4589cfa7f2 in ?? () from /usr/lib/x86_64-linux-gnu/libkrb5.so.3
#3  0x00007f4589cfb094 in ?? () from /usr/lib/x86_64-linux-gnu/libkrb5.so.3
#4  0x00007f4589cfb50c in krb5_sendto_kdc ()
   from /usr/lib/x86_64-linux-gnu/libkrb5.so.3
#5  0x00007f4589cd1565 in krb5_tkt_creds_get ()
   from /usr/lib/x86_64-linux-gnu/libkrb5.so.3
#6  0x00007f4589cd16cd in krb5_get_credentials ()
   from /usr/lib/x86_64-linux-gnu/libkrb5.so.3
#7  0x00007f458b20e595 in smb_krb5_get_credentials (context=0x7f458ca623d0, 
    ccache=<optimized out>, me=<optimized out>, server=<optimized out>, 
    impersonate_princ=<optimized out>, out_creds=0x7fff8e06b048)
    at libsmb/clikrb5.c:2020
#8  0x00007f458b20eb1d in ads_krb5_mk_req (impersonate_princ_s=0x0, 
    expire_time=0x7f458ca36ac8, outbuf=0x7fff8e06b000, ccache=0x7f458ca6e330, 
    principal=0x7f458ca62360 "ldap/dc-3.ad.example.com@AD.EXAMPLE.COM", ap_req_options=1, auth_context=0x7fff8e06b030, context=0x7f458ca623d0)
    at libsmb/clikrb5.c:704
#9  cli_krb5_get_ticket (mem_ctx=0x7f458ca31110, 
    principal=0x7f458ca62360 "ldap/dc-3.ad.example@AD.EXAMPLE.COM", time_offset=<optimized out>, ticket=0x7fff8e06b0e0, 
    session_key_krb5=0x7fff8e06b170, extra_ap_opts=0, 
    ccname=0x7f458ca63060 "MEMORY:net_ads", tgs_expire=0x7f458ca36ac8, 
    impersonate_princ_s=0x0) at libsmb/clikrb5.c:904
#10 0x00007f458b210084 in spnego_gen_krb5_negTokenInit (ctx=0x7f458ca31110, 
    principal=<optimized out>, time_offset=<optimized out>, 
    targ=0x7fff8e06b150, session_key_krb5=<optimized out>, 
    extra_ap_opts=<optimized out>, expire_time=0x7f458ca36ac8)
    at libsmb/clispnego.c:311
#11 0x00007f458b52c2c1 in ads_sasl_spnego_rawkrb5_bind (ads=0x7f458ca36a70, 
    principal=<optimized out>) at libads/sasl.c:783
#12 0x00007f458b52ce3f in ads_sasl_spnego_krb5_bind (p=0x7fff8e06b2a0, 
    ads=0x7f458ca36a70) at libads/sasl.c:823
#13 ads_sasl_spnego_krb5_bind (p=0x7fff8e06b2a0, ads=0x7f458ca36a70)
    at libads/sasl.c:1233
#14 ads_sasl_spnego_bind (ads=0x7f458ca36a70) at libads/sasl.c:904
#15 0x00007f458b52d50a in ads_sasl_bind (ads=0x7f458ca36a70)
    at libads/sasl.c:1213
#16 0x00007f458b5282c0 in ads_connect (ads=0x7f458ca36a70) at libads/ldap.c:730
#17 0x00007f458b0f7ff3 in ads_startup_int (c=0x7f458ca31170, 
    only_own_domain=true, auth_flags=0, ads_ret=0x7fff8e06b7d8)
    at utils/net_ads.c:292
#18 0x00007f458b0f8ca2 in ads_startup (c=<optimized out>, 
    only_own_domain=<optimized out>, ads=<optimized out>)
    at utils/net_ads.c:339
#19 0x00007f458b0faa5f in net_ads_join_ok (c=0x7f458ca31170)
    at utils/net_ads.c:1056
#20 0x00007f458b0fab0a in net_ads_testjoin (c=0x7f458ca31170, 
    argc=<optimized out>, argv=<optimized out>) at utils/net_ads.c:1083
#21 0x00007f458b0fd114 in net_ads (c=<optimized out>, argc=<optimized out>, 
    argv=<optimized out>) at utils/net_ads.c:2812
#22 0x00007f458b0f636b in main (argc=<optimized out>, argv=<optimized out>)
    at utils/net.c:939
(gdb) detach

Core dump of the process is attached as well.